How to spot spray broadleaf weeds in a lawn

A lawn with a dozen dandelions doesn’t need the whole area sprayed. Spot spraying puts herbicide only where the weeds are, which means less product, less cost, and less stress on the grass. It’s also the safest way to treat weeds in grasses that are sensitive to herbicides, such as buffalo.

The catch is accuracy. A herbicide that’s safe on your lawn can still kill the roses next to it, and a weed killer that isn’t safe on your grass will leave a dead patch wherever you spot spray. This guide covers identifying the weed, choosing the right product, spraying precisely and following up.

Identify the weed first

Herbicides only work on the weeds their labels list. Before you buy anything, work out what you have. The Weed Identifier can help.

Lawn weeds fall into a few broad groups:

• Broadleaf weeds have wider leaves with a network of veins, and often flowers. Bindii, clover, dandelion and cudweed are common examples. Selective broadleaf herbicides are made for these.
• Grass weeds, such as winter grass and summer grass, are grasses themselves. Broadleaf herbicides won’t touch them. See the pre-emergent guide and the winter grass answers.
• Sedges, such as nutgrass, look like grass but have triangular stems. They need products whose labels list them.
• Bulb weeds, such as onion weed, grow from bulbs that most sprays don’t reach well. Digging out the whole clump is often the most reliable method.

If you’re not sure, take a sample to a garden centre or compare it with the Lawn Library entries before you spray.

Choose a product that’s safe on your grass

Look for a selective herbicide: one that kills certain weeds without killing the lawn. The label must list:

• your grass type, as a situation where the product can be used; and
• the weed you want to control.

If either is missing, don’t use it on your lawn.

Buffalo needs particular care. It is more sensitive to some herbicides than other lawn grasses, and labels may say so. One registered MCPA product’s label, for example, warns that buffalo grass is more easily damaged than other grasses. Use only products whose labels list buffalo, and follow their directions exactly.

Dicamba and MCPA, two active ingredients found in lawn broadleaf herbicides, are Group 4 herbicides, which mimic plant growth hormones. CropLife Australia’s mode-of-action table groups herbicides this way, which helps if you need to rotate products for a persistent weed.

Non-selective herbicides, such as glyphosate, kill grass as well as weeds. They’re for weeds in paths, driveways and areas you plan to replant, not for spot spraying a lawn, unless you’re prepared to repair a dead patch.

If you’re unsure whether a product is registered for your use, search for it on the APVMA’s PubCRIS database, which links to the approved label.

When to spray

• While weeds are young and actively growing. Small weeds absorb herbicide well and die more readily. Bindii, for example, grows over winter and forms prickly burrs in spring, so the time to deal with it is in winter, before it seeds.
• When the lawn isn’t stressed. Avoid spraying lawns stressed by heat, drought or waterlogging, and check the label for temperature limits.
• Not on new turf or seed until the label says the lawn is established enough.
• On a calm, dry day. You need little or no wind and no rain within the label’s rain-free period.
• Check the label for mowing directions. Many say not to mow for a short time before and after spraying.

Protect bees

Bees forage on flowering weeds such as clover. BeeAware, Plant Health Australia’s bee biosecurity program, recommends mowing flowering weeds in the target area before spraying, so fewer bees are feeding there when you spray. Follow any bee warnings on the label, and keep spray off flowering plants nearby.

Choosing the equipment

• A ready-to-use trigger pack is the simplest option for a handful of weeds. The product is already diluted, so there’s nothing to measure.
• A pump-up sprayer with an adjustable cone nozzle suits larger areas or many scattered weeds. Keep it only for herbicides, and label it.
• A spray shield (a cone or hood around the nozzle) stops droplets escaping sideways. It’s especially useful along garden edges.

Whatever you use, check it doesn’t leak, and check the nozzle gives a fine, even cone rather than a jet. The sprayer calibration guide shows how to check a nozzle.

Mixing

Labels often give a separate dilution for spot spraying, as an amount of product for each litre of water. Use exactly that.

1. Read the mixing directions. Some labels say to half-fill the sprayer with water, add the product, then top up.
2. Mix outdoors, on a hard surface away from drains, children, pets and garden beds.
3. Wear the protective equipment the label lists while you handle the concentrate.
4. Measure accurately with a measuring cylinder kept only for chemicals. Never use kitchen utensils.
5. Mix only what you need for today. A litre or two goes a long way when you’re spot spraying.

A stronger mix doesn’t kill weeds faster. It’s more likely to damage the lawn, and using a product other than as its label directs can be illegal.

How to spot spray

1. Plan your route. Walk the lawn in strips, as you would when mowing, so you don’t miss weeds or spray any twice.
2. Keep the nozzle low and close to the weed, pointing down, so the spray lands on the leaves and nowhere else.
3. Wet the leaves evenly, as the label directs. Most say to wet the foliage, not to spray until the mix drips off. Extra spray runs into the soil around the weed and onto the grass.
4. Spray the whole weed, not just the centre. Weeds with rosettes, such as dandelion, need all their leaves covered.
5. Use short bursts. Release the trigger between weeds.
6. Keep pumping to hold the pressure steady. High pressure makes fine droplets that drift.
7. Treat a patch, not a lawn. If you find yourself spraying every square metre, stop and consider whether a broadcast application at the label rate would be more appropriate.

Weeds near garden beds

Lawn edges are where most accidental damage happens.

• Use a spray shield, or hold a piece of cardboard between the weed and the garden bed.
• Spray with the nozzle angled away from the bed.
• Leave weeds right against prized plants to dig out by hand.
• On a breezy day, leave the edges for another time.

Weeds in paths and on hard surfaces

Herbicide that lands on concrete or pavers can wash into stormwater drains. Spray carefully, use the least amount that wets the weed, and check the label allows use on that surface.

After spraying

• Keep people and pets off the treated area for as long as the label says, at least until the spray has dried.
• Don’t water or mow until the time on the label has passed.
• Rinse the sprayer as the label directs, and spray the rinse water onto the treated area if the label allows it. Never pour it down the sink or drain.
• Wash your gloves before taking them off, then wash your hands.
• Store the product in its original container, locked away from children and pets.

What to expect

Herbicides that mimic growth hormones often make weeds twist, curl and yellow before they die. Depending on the product, the weed and the weather, it can take days to weeks for them to die completely. Don’t re-spray just because weeds still look alive after a few days. Check the label for when, or whether, you can re-treat.

When weeds die, they leave small bare spots. Grasses that spread by runners, such as buffalo, couch, kikuyu and zoysia, usually fill these in during the growing season. If they don’t, a little topdressing helps.

Non-chemical options

For a small number of weeds, removing them by hand is often quicker than mixing a spray.

• Dig out weeds with tap roots, such as dandelion, with a narrow trowel or weeding tool, getting as much root as you can.
• Lift bindii plants in winter, while they’re small and before they form burrs.
• Dig out clumps of onion weed, including every tiny bulblet, and bag them for the bin rather than the compost.
• Feed the lawn. Clover makes its own nitrogen through its roots, so it does well in lawns that are short of it. A well-fed lawn competes better.
• Mow at the right height. A dense lawn shades the soil and leaves less room for weeds to germinate.

Common lawn weeds at a glance

Common mistakes

• Spraying before identifying the weed.
• Using a product whose label doesn’t list your grass, especially on buffalo.
• Spraying to run-off, which puts more herbicide on the soil and surrounding grass.
• Making the mix stronger to get faster results.
• Spraying in wind or just before rain.
• Re-spraying too soon, before the first treatment has had time to work.
• Using the same sprayer for herbicides and fertilisers.

Log it

Log each spray in your Lawn Journal: the product, the weeds, the area treated and the date. When you check results a few weeks later, add a note. Over a season or two, you’ll see which weeds keep coming back and where, which often points to a lawn that’s thin, compacted or short of food in that area.